Many modern electronic devices include wireless communications circuitry. For example, an electronic device may include wireless local area network (WLAN) communications circuitry, cellular communications circuitry, or the like. While wireless communications circuitry allows electronic devices to communicate with one another, such functionality generally comes at the cost of additional energy consumption and thus reduced battery life. Often, wireless communications circuitry is the largest consumer of energy in an electronics device. As wireless communications protocols evolve to provide higher speeds, energy consumption of communications circuitry often increases to meet the higher demands of such protocols.
Consumer demand for longer battery life from electronic devices has resulted in the development of many power-saving techniques for wireless communications. One way to conserve power consumed via wireless communications is through the use of envelope tracking. Envelope tracking involves modulating a supply voltage provided to an amplifier based on the instantaneous magnitude (i.e., the envelope) of an RF input signal provided to the amplifier. FIG. 1 illustrates the basic concept of envelope tracking. Specifically, FIG. 1 shows an amplitude-modulated RF signal 10. Conventionally, a constant supply voltage at a level sufficient to ensure adequate headroom across the entire amplitude range of the RF signal 10 would be supplied to an RF amplifier, as shown by line 12. This results in a significant amount of wasted energy, and thus poor efficiency, when the amplitude of the RF carrier is below the maximum level, as illustrated by line 14. Accordingly, an envelope power supply signal tracks the amplitude of the RF signal 10, as illustrated by line 16, and therefore increases efficiency by preventing the unnecessary expenditure of power when the amplitude of the RF signal 10 is below the maximum level.
While envelope tracking is a good way to decrease energy expenditure associated with wireless communications circuitry, it may not be compatible with wireless communications applications including strict timing requirements. For example, modern WLAN protocols generally require a transmitter to transition from an off-state to a transmit-state in less than ˜10 μs. Further, the transmitter generally does not know the target output power until less than ˜3 μs before transmission occurs. Generally, these stringent timing requirements are not problematic in transmitter applications that do not utilize envelope tracking, because the supply voltage to the transmitter is simply the battery voltage (which can be nearly instantaneously connected or disconnected to the transmitter). However, envelope power converter circuitry used to provide an envelope power supply signal to the transmitter generally utilizes switching power converter circuitry including significantly large inductive and capacitive elements. As will be appreciated by those of ordinary skill in the art, these inductive and capacitive elements restrict the ability of the envelope power converter circuitry to instantaneously provide a particular envelope power supply signal and therefore meet the timing requirements discussed above. Accordingly, envelope tracking has experienced slow adoption in WLAN applications and other wireless communications protocols with strict timing requirements.
In light of the above, there is a need for envelope tracking methods and apparati that are compatible with wireless communications protocols including strict timing requirements.